In the fluid mechanics it is known that the efficiency of the cloth sails is lower than the wings of the aeroplanes. In these wings, the difference between the lift strength and the weight permits the aeroplane to flight, because the aerodynamic limit layer of the air does not come off the profile. On the contrary, in the conventional sails in the naval sector, it the wind push which inflates the sail and produces, by thrust, a resulting strength that permits the advancement of the ship or vessel.
During long time a sail for aquatic navigation presenting the advantages of the aviation wings has been desired. To this end, there have been some attempts to provide rigid sails with an aerodynamic profile of aeronautic kind
Among them it must be cited the Flettner rotors already disclosed in 1926 by Anton Flettner (FLETTNER, Anton, “Mein Weg zum Rotor”, Leipzig (Köhler & Amelang, 1926)), cited e.g. in EP 040 597.
WO 2004024556 discloses a rigid sail comprising two parts that can be relatively rotated about a vertical axis to determine the intrados and extrados of a sail like an aerodynamic profile of those used for the wings of the aeronautic technics.
WO 0189923 discloses a rigid sail with a hinged aerodynamic profile that comprises three vertical elements (or modules), each of them being formed by three horizontal elements (or sections) hinged to each other or extrados from the rigid wing or sail.
U.S. Pat. No. 7,146,918 discloses a system for generating electric power and hydrogen from sea water and wind power, in systems floating in water comprising rigid sails.
FR 2648426 discloses a wing comprising a rigid part and a flexible part that houses inside a housing in the rigid part, permitting different aerodynamic configurations.
ES 2311399 discloses a rigid sail with a configurable profile, with closing elastic sheets, joined to the corresponding wall in at least a zone close to said end edge and means for generating and feeding pressurized air and vacuum to inflate and deflate the sails to voluntarily change the profile of the sail.
However, these attempts, from which only some illustrative examples have been cited, have not achieved yet a versatile, cheap and easy operated device. The object of the present invention is to provide a solution to this need.